Ultraviolet absorbing glasses

ABSTRACT

A non-photochromic R 2  O--B 2  O 3  --SiO 2  glass containing a cuprous or cuprous-cadmium halide crystal phase, having a sharp spectral cutoff at about 400 nm, the glass composition consisting essentially of, in cation percent, 35-73% SiO 2 , 15-45% B 2  O 3 , 0-12% Al 2  O 3 , the Al 2  O 3  being less than 10% when the SiO 2  is over 55%, 0-12% Li 2  O, O-20% Na 2  O, 0-12% K 2  O, the Li 2  O+Na 2  O+K 2  O being 4.75-20%, 0-5% CaO+BaO+SrO, 0.125-1.0% Cu 2  O, 0-1% CdO, 0-5% ZrO 2 , 0-0.75% SnO 2 , 0-1% As 2  O 3  and/or Sb 2  O 3 , the glass containing 0-1.75% Cl, 0-1.0% Br, 0.25-2.0% Cl+Br and 0-2% F by weight, and having an R-value, calculated in mole percent of 0.15-0.45, the R-value not exceeding 0.30, except as the glass composition meets at least one condition selected from the group: up to 12 cation % Li 2  O, less than 10 cation % Al 2  O 3 , at least 0.3 cation % Cu 2  O and 0.50-2.0% Cl+Br. 
     Also, a method of making the non-photochromic glass having a sharp spectral cutoff.

This application is a continuation-in-part application of Ser. No.07/917,761, filed Jul. 21, 1992, now abandoned.

FIELD OF THE INVENTION

The field is a family of glasses that strongly absorb ultravioletradiation, but are non-photochromic and may be essentially colorless.

BACKGROUND OF THE INVENTION

Recently, a great deal of attention has been directed to the harmfuleffects of ultraviolet (UV) radiation on humans. Much of the attentionhas concerned the effect of such radiation on the eye. Accordingly, thevalue of strong UV absorption by eye glasses has been recognized.

It is well known that UV radiation can also cause degradation anddiscoloration in such items as paints, fabrics and plastics. Therefore,strong UV absorption by architectural glazing materials is beneficial.The sun is not the only light source that emits UV. Various types ofartificial lighting, such as halogen lamps, may also emit UV radiation.Accordingly, there is an interest in minimizing UV radiation emitted byartificial sources as well. This may be achieved by utilizing UVabsorbing glass in the fabrication of lamp envelopes, reflectors andlenses.

It is common knowledge that photochromic glasses are activated byabsorption of UV radiation. The most evident utility of such glasses hasbeen in control of visible light transmission. Inherently, however, theyalso strongly influence the intensity of UV transmission. This behavioris readily understood in terms of the Grotthus-Draper Law which statesthat: Only light that is absorbed can produce chemical change

Photochromic glasses containing silver halide crystals absorb stronglyat wavelengths shorter than 320 nm, but only weakly in the intervalbetween 320 and 400 nm. Radiation in the wavelength range of 320-400 nmis much less harmful than that in the shorter wavelength region.Nevertheless, for some purposes, it would be desirable to eliminatetransmission of this radiation as well. Therefore, it has been proposedto dope the above glasses with ions which provide additional absorptionof UV radiation.

Photochromic glasses containing halides of copper and/or cadmium arealso known, but not commercially available. Such glasses were originallydisclosed in U.S. Pat. No. 3,325,299 (Araujo). The transmission cutoffin these glasses occurs at approximately 400 nm, and is much sharperthan that in silver halide glasses. Consequently, protection against UVradiation is complete in these glasses without additional doping. We areunaware of any other material that provides such a sharp transmissioncutoff at the precise line between visible and UV radiation. Theprecipitation of the copper halide phase in these glasses is like thatof the silver halide phase in the silver halide photochromic glasses. Itmay require heating of a glass containing in solution the copper andhalogen ions of interest. As taught in the patent, the glass ismaintained for a short time at a temperature somewhat above theannealing point

There are numerous applications for glasses having the sharp UV cutoffinherent in the copper or copper-cadmium halide glasses. Frequently,however, such applications require avoiding any change in visibleabsorption such as occurs in photochromic glasses exposed to UVradiation, e.g., sunlight. Therefore, it would be highly desirable toachieve the sharp UV cutoff characteristic of the copper andcopper-cadmium halide glasses without the attendant photochromicbehavior. It would also be highly desirable to produce such glasses thatare essentially colorless because the yellow color associated with mostUV absorbing materials is unacceptable for many applications. However,various fixed colors are desirable for other applications.

It is a basic purpose of the present invention to provide UV absorbingglasses that are not photochromic. A further purpose is to provideglasses that exhibit a sharp cutoff in transmission in the wavelengthinterval separating visible and UV radiation. Another purpose is toprovide a glass in which a desired visible color may be obtained withoutdiminution of the strength of the UV absorption.

SUMMARY OF THE INVENTION

Our invention resides in a non-photochromic R₂ O--B₂ O₃ --SiO₂ glasswhich contains a precipitated cuprous or cuprous-cadmium halide crystalphase and has a sharp spectral cutoff at about 400 nm, the glasscomposition consisting essentially of, in cation percent, 35-73% SiO₂,15-45% B₂ O₃, 0-12% Al₂ O₃, the Al₂ O₃ being less than 10% when the SiO₂is over 55%, 0-12% Li₂ O, 0-20% Na₂ O, 0-12% K₂ O, the Li₂ O+Na₂ O+K₂ Obeing 4.75-20%, 0.5% CaO+BaO+SrO, 0.125-1.0% Cu₂ O, 0-1% CdO, 0-5% ZrO₂,0-0.75% SnO₂, 0-1% As₂ O₃ and/or Sb₂ O₃, the glass containing 0-1.25%Cl, 0-1.0% Br, 0.25-2.0% Cl+Br and 0-2% F by weight, and having anR-value, calculated in mole percent, of about 0.15-0.45, the R-value notexceeding 0.30, except as the glass composition meets at least onecondition selected from the group up to 12 cation % Li₂, less than 10cation % Al₂ O₃, at least 0.3 cation % Cu₂ O and 0.50-2.0% Cl+Br.Cadmium is not required to secure absorption of ultraviolet radiation.Whereas CdO complements the action of Cu₂ O, it provides no exceptionalbenefit which can compensate for the hazards faced in its use due to itsextreme toxicity. Moreover, CdO can promote photochromism, whichphenomenon is unwanted in the present invention. Therefore, the amountincluded should be strictly restricted, i.e., not more than 1% and,preferably, not more than 0.5%.

In order to assure that the glass exhibits good chemical durability, Al₂O₃ will be included therein in an amount of at least 0.25%. Thepreferred glass compositions consist essentially, expressed in cationpercent, of 40-70% SiO₂, the Al₂ O₃ being less than 10% when the SiO₂ isover 55%, 0-12% Li2O, 0-20% Na₂ O, 0-12% K₂ O, the Li₂ O+Na₂ O+K₂ Obeing 8-20%, 0-5% CaO+BaO+SrO, 0.2-0.5% Cu₂ O, 0-5% ZrO₂ 0-0.5% SnO₂,0-1% As₂ O₃ and/or Sb₂ O₃, the glass containing 0-1.0% Cl, 0-1.0% Br,0.5-1.5% Cl+Br, and 0-2% F by weight, and having an R-value, calculatedin mole percent, of 0.15-0.45, the R-value note exceeding 0.30, exceptas the glass composition meets at least one condition selected from thegroup: up to 12 cation % Li₂ O, less than 10 cation % Al₂ O₃, at least0.3 cation % Cu₂ O, and 0.5-1.5% Cl+Br.

PRIOR ART

In addition to the art earlier cited, attention is also directed to thefollowing patent literature:

U.S. Pat. No. 4,166,745 (Araujo et al.) discloses copper-cadmiumphotochromic glasses that have a refractive index of 1.52-1.54, and thatmay be strengthened by an exchange of sodium ions for lithium ions.

U.S. Pat. No. 4,222,781 (Morse et al.) discloses photochromic glassesbased on copper halide wherein good optical clarity and photochromicproperties are provided by controlling the alkali metal oxide, the Al₂O₃ and the B₂ O₃ concentrations in the base glass, and/or by adding MoO₃or WO₃ to the composition.

European Publication Number 0 456 351 A2 [U.S. Pat. No, 5,145,805](Tarumi et al) discloses two glass families containing up to 15% copperhalide. The non-phosphate family comprises, in percent by weight, 20-85%SiO₂, 2-75% B₂ O₃, up to 15% Al₂ O₃, up to 30% alkali metal oxides, upto 10% divalent metal oxides and up to 10% of at least one of ZrO₂, La₂O₃, Y₂ O₃, Ta₂ O₃ and Gd₂ O₃. The broad ranges of this disclosure failto disclose critical features of the present invention.

BRIEF DESCRIPTION OF THE DRAWING

The single FIGURE in the attached drawign is a graphical representationcomparing the UV Absorption spectra for three glasses.

DESCRIPTION OF THE INVENTION

The present invention is based on our discovery of a family of R₂ O--B₂O₃ --SiO₂ glasses that contain a cuprous or cuprous-cadmium halidecrystal-phase, that are non-photochromic, that are transparent tovisible radiation and that have a sharp transmission cutoff between thevisible and UV radiation ranges; that is, at about 400 nm. As in thecase of the photochromic glasses, the precipitation of the halidecrystal phase may require an additional heat treatment after the glassobject has been formed. In a preferred embodiment, the glasses areuncolored; that is, they are free of any fixed tint. The invention isfurther based on the discovery of the composition parameters necessaryto produce such glasses

An initial consideration is precipitation of a cuprous halide crystalphase. This is essential to provide the desired sharp transmissioncutoff. For this purpose the glass should contain, in its composition,at least 0.125 cation percent cuprous oxide (Cu₂ O). The content mayrange up to about one percent, but cuprous ions tend to disproportionateinto cupric ions and neutral atoms at such higher contents. Therefore,we prefer to use no more than about 0.5%.

Absorption in the red part of the spectrum resulting in the developmentof a blue-green coloration in the glass is associated with thetransitions between "d" states in a cupric (Cu⁺²) ion. The "d" statesare completely occupied in a cuprous (Cu⁺²) ion. Therefore, this ioncontributes no visible color. Since only the cuprous ion is required forthe formation of cuprous halides, colorless glasses with a sharp UVcutoff may be obtained by appropriate adjustment of the oxidation stateof the copper.

The oxidation state of the copper observed in glass is influenced by thetemperature of the melt, by the partial pressure of oxygen to which themelt is exposed, by the concentrations of polyvalent ions in the glass,and by the basicity (the R-value) of the glass. As₂ O₃, Sb₂ O₃ and SnO₂are polyvalent metal oxides which are especially useful because they donot directly impart color to the glass. Nevertheless, care must be usedin the choice of reducing agent and the amount used.

Studies have indicated that arsenic is only weakly reducing with respectto the cuprous/cupric oxidation couple, and does not reduce cuprous ionsto neutral atoms. However, in the presence of high concentrations offluorine, arsenic promotes the precipitation of cupric oxide crystalswhich impart a strong orange color to the glass. In contrast, tin tendsto strongly reduce cupric ions and can, in high concentrations, reducethe copper all the way to the metal. Colloidal copper metal imparts ared color to the glass. The behavior of antimony oxide is similar tothat of tin oxide.

In addition to copper in the cuprous state, at least 0.25% by weight ofchlorine or bromine is necessary to combine with the copper to form therequired crystal phase. The presence of F may be helpful, but does notproduce a cuprous halide phase in the absence of other halogens. Thehalides are expressed in weight percent, since they obviously do notlend themselves to expression in cation percent. The remainder of thecomposition components are expressed in cation percent because of thedisparity in atomic weights of the cations.

A particularly significant control factor is what has come to be knownas the R-value. This value is a measure of basicity of a glass, and isdefined by the formula: ##EQU1## where M₂ O represents alkali metaloxides and MO represents alkaline earth metal oxides. Precipitation of acuprous halide crystal phase has been observed in glasses having anR-value below 0.15. However, no particular advantage was seen in suchglasses, and they tend to be difficult to melt, or to exhibit poorchemical durability.

In most cases, the R-value should not exceed about 0.35. However, thevalue may be extended as high as 0.45 by control of other components.These include employing a LiO₂ O level up to 12 cation percent,maintaining the Al₂ O₃ level below 10%, employing over 0.3% Cu₂ O and/orCl+Br levels up to 1.5%. In general, however, we find that optimumphysical properties, in conjunction with good UV absorption, areobserved when the R-value is approximately 0.25. That value may beconsidered an optimal value.

As mentioned above, the blue-green color associated with the cupric ionabsorbing in the red part of the spectrum may be avoided by chemicallyreducing the copper to the cuprous state. In the circumstance that agreen color is desired, it may be obtained by incomplete reduction. Ofcourse, small amounts (up to about 1%) of the transition metal ions orrare earth ions commonly used as colorants in the glass art may be usedto impart color without deleterious affects. It has already beenmentioned that use of large amounts of arsenic, antimony or tin oxidesmay produce orange, brown or red glasses While colorless glasses arepreferred in many circumstances, there may be applications in which thecolors produced by high levels of reducing agents are desirable.

Any of the materials, such as titania, zirconia, niobia, lead oxide, andthe alkaline earth metal oxides, which have been used to raise therefractive index of a glass, can be used in small amounts withoutserious sacrifice of UV absorption. Many of these materials, such asTiO₂, give rise to a moderate to strong yellow or gold color in thepresence of copper in those glasses having an R-value conducive to theprecipitation of copper chloride. Zirconia and the alkaline earths areespecially useful in that they do not contribute to such a yellow colorand may be used in amounts up to about 5 cation %. This factor isimportant because a high value of the refractive index is required forophthalmic lenses, the usual standard being 1.523. If CaO and/or BaO areemployed, it is preferred that they be roughly equal in amount since CaOalone may lead to opacity and BaO alone may inhibit precipitation of thehalide phase.

Whereas MoO₃ and WO₃ can be included to adjust the refractive index ofthe glasses without a deleterious effect upon the capability of theglasses to absorb ultraviolet radiation, the amounts of those oxidesought to be held at levels below about 0.5 cation percent because theyenhance photochromism which the present inventive compositions aredesigned to suppress.

In glasses which are photochromic because of the presence of copperhalides, the UV absorption may be retained and the photochromismsuppressed, or totally eliminated, by several simple compositionadjustments. A slight diminution of copper will eliminate photochromismwithout a serious sacrifice of UV absorption. Alternatively, an increasein the concentrations of chloride and bromide, possibly accompanied by adecrease in the concentration of fluoride, eliminates photochromism atordinary temperatures.

The invention is further described with reference to specificembodiments TABLE 1A sets forth in cation percent, except for thehalogens which are necessarily in weight percent, the compositions ofseveral glasses These glasses exhibit a sharp UV transmission cutoffthat is characteristic of a copper halide crystal phase. Moreover, theyare non-photochromic and exhibit no fixed tint. Glasses 5 and 7illustrate the use of Zr02 to enhance refractive index while avoidingintroduction of a yellow color. The R-values for the glasses are alsoshown.

TABLE 1B sets forth the same glass compositions as in TABLE 1A, exceptin weight percent. The base composition (exclusive of halogens, copperand tin oxides) equals or approximates 100 in TABLE 1A. The entirecomposition approximates 100 in TABLE 1B. The same will be true inTABLES 2A and 2B. CuO was employed as the batch material, the presenceof reducing agents in the batch assuring the reduction thereof to Cu₂ O.Cu₂ O comprises about 56% of a concentration of CuO.

                                      TABLE 1A                                    __________________________________________________________________________    1        2   3   4   5   6   7   8   9   10                                   __________________________________________________________________________    SiO.sub.2                                                                          42.5                                                                              42.5                                                                              49.0                                                                              49.0                                                                              46.0                                                                              65  45.5                                                                              37.5                                                                              70.0                                                                              71.3                                 Al.sub.2 O.sub.3                                                                   7.5 7.5 9.0 9.0 4.5 2.5 9.0 2.5 2.0 2.1                                  B.sub.2 O.sub.3                                                                    32.75                                                                             34.0                                                                              22.8                                                                              22.8                                                                              26.7                                                                              23.5                                                                              27.8                                                                              44.2                                                                              21.2                                                                              19.8                                 Li.sub.2 O                                                                         12.0                                                                              5.25                                                                              7.0 7.0 3.5 --  6.0 --  --  --                                   Na.sub.2 O                                                                         5.25                                                                              10.8                                                                              10.8                                                                              0.5 13.25                                                                             9.0 6.8 15.8                                                                              6.78                                                                              6.8                                  K.sub.2 O                                                                          --  --  0.75                                                                              11.0                                                                              1.5 --  3.0 --  --  --                                   WO.sub.3                                                                           --  --  0.35                                                                              0.35                                                                              --  --  --  --  --  --                                   ZrO.sub.2                                                                          --  --  --  --  4.5 --  2.0 --  --  --                                   SnO.sub.2                                                                          0.18                                                                              0.18                                                                              --  --  0.35                                                                              0.25                                                                              0.16                                                                              0.18                                                                              0.20                                                                              0.12                                 As.sub.2 O.sub.3                                                                   --  --  0.35                                                                              0.35                                                                              --  --  --  --  --  --                                   CuO  0.25                                                                              0.25                                                                              0.30                                                                              0.30                                                                              0.50                                                                              0.28                                                                              0.25                                                                              0.28                                                                              0.32                                                                              0.27                                 Cl   0.60                                                                              0.60                                                                              0.40                                                                              0.40                                                                              0.60                                                                              0.75                                                                              0.50                                                                              0.74                                                                              0.88                                                                              0.73                                 Br   0.40                                                                              0.40                                                                              0.35                                                                              0.35                                                                              0.40                                                                              0.50                                                                              0.50                                                                              0.49                                                                              0.49                                                                              0.49                                 F    --  --  --  --  1.8 0.75                                                                              --  --  0.78                                                                              0.73                                 R-   0.30                                                                              0.25                                                                              0.41                                                                              0.41                                                                              0.35                                                                              0.27                                                                              0.17                                                                              0.30                                                                              0.22                                                                              0.24                                 value                                                                         __________________________________________________________________________

                                      TABLE 1B                                    __________________________________________________________________________    1        2   3   4   5   6   7   8   9   10                                   __________________________________________________________________________    SiO.sub.2                                                                          56.6                                                                              55.2                                                                              60.7                                                                              58.7                                                                              52.6                                                                              73.8                                                                              55.3                                                                              49.9                                                                              77.5                                                                              78.8                                 Al.sub.2 O.sub.3                                                                   8.5 8.3 9.5 9.1 4.4 2.4 9.3 2.8 1.9 1.9                                  B.sub.2 O.sub.3                                                                    25.3                                                                              25.6                                                                              16.4                                                                              15.8                                                                              17.7                                                                              15.5                                                                              19.6                                                                              34.1                                                                              13.6                                                                              12.6                                 Li.sub.2 O                                                                         4.0 1.7 2.2 2.1 1.0 --  1.8 --  --  --                                   Na.sub.2 O                                                                         3.6 7.2 6.9 0.31                                                                              7.8 5.3 4.3 10.8                                                                              3.9 3.9                                  K.sub.2 O                                                                          --  --  0.73                                                                              10.3                                                                              1.3 --  2.9 --  --  --                                   WO.sub.3                                                                           --  --  1.7 1.6 --  --  --  --  --  --                                   ZrO.sub.2                                                                          --  --  --  --  10.6                                                                              --  5.0 --  --  --                                   SnO.sub.2                                                                          0.57                                                                              0.57                                                                              --  --  1.0 0.71                                                                              0.49                                                                              0.58                                                                              0.55                                                                              0.35                                 As.sub.2 O.sub.3                                                                   --  --  0.71                                                                              0.69                                                                              --  --  --  --  --  --                                   CuO  0.44                                                                              0.43                                                                              0.49                                                                              0.48                                                                              0.76                                                                              0.41                                                                              0.40                                                                              0.48                                                                              0.48                                                                              0.40                                 Cl   0.60                                                                              0.60                                                                              0.40                                                                              0.40                                                                              0.60                                                                              0.75                                                                              0.50                                                                              0.74                                                                              0.88                                                                              0.73                                 Br   0.40                                                                              0.40                                                                              0.35                                                                              0.35                                                                              0.40                                                                              0.50                                                                              0.50                                                                              0.49                                                                              0.49                                                                              0.49                                 F    --  --  --  --  1.8 0.75                                                                              --  --  0.78                                                                              0.75                                 __________________________________________________________________________

TABLE 2A sets forth in cation percent, again except for the halogens,the compositions of several glasses. These glasses also exhibit a sharpUV transmission cutoff characteristic of a copper halide crystal phaseand are non-photochromic. However, they do exhibit a fixed tint asindicated. The R-values for these glasses are included in the TABLE.

TABLE 2B sets forth the glass compositions of TABLE 2A in weightpercent.

                                      TABLE 2A                                    __________________________________________________________________________    11      12  13  14  15 16  17  18  19  20                                     __________________________________________________________________________    SiO.sub.2                                                                         47  47  46  46  42.5                                                                             42.5                                                                              46  63.1                                                                              69.2                                                                              68.3                                   Al.sub.2 O.sub.3                                                                  9   9   9   9   7.5                                                                              7.5 9   0.25                                                                              1.8 2.1                                    B.sub.2 O.sub.3                                                                   30  27  26.7                                                                              26.7                                                                              32.75                                                                            32.75                                                                             26.7                                                                              31.7                                                                              21.3                                                                              21.9                                   Li.sub.2 O                                                                        --  5   3.5 3.5 -- 8.0 3.5 1.5 --  --                                     Na.sub.2 O                                                                        14  7   13.3                                                                              13.3                                                                              17.25                                                                            9.25                                                                              13.3                                                                              2.0 7.6 7.8                                    K.sub.2 O                                                                         --  5   1.5 1.5 -- --  1.5 1.5 --  --                                     WO.sub.3                                                                          0.35                                                                              0.35                                                                              --  --  -- --  --  --  --  --                                     SnO.sub.2                                                                         0.10                                                                              0.10                                                                              0.3 0.17                                                                              0.18                                                                             0.18                                                                              0.20                                                                              0.20                                                                              0.13                                                                              0.13                                   CuO 0.25                                                                              0.25                                                                              0.5 0.5 0.25                                                                             0.25                                                                              0.50                                                                              0.35                                                                              0.28                                                                              0.28                                   Cl  0.60                                                                              0.60                                                                              0.25                                                                              0.25                                                                              0.60                                                                             0.60                                                                              --  0.98                                                                              0.74                                                                              0.74                                   Br  0.40                                                                              0.40                                                                              0.25                                                                              0.25                                                                              0.40                                                                             0.40                                                                              0.50                                                                              0.74                                                                              0.49                                                                              0.49                                   F   --  --  1.85                                                                              1.85                                                                              -- --  --  --  0.74                                                                              0.74                                   R-  0.17                                                                              0.30                                                                              0.35                                                                              0.35                                                                              0.30                                                                             0.30                                                                              0.35                                                                              0.15                                                                              0.28                                                                              0.26                                   value                                                                         Color                                                                             Yellow                                                                            Green                                                                             Deep                                                                              Dark                                                                              Red                                                                              Light                                                                             Light                                                                             Pink                                                                              Purple                                                                            Pink                                               Red Green  Pink                                                                              Green                                              __________________________________________________________________________

                                      TABLE 2B                                    __________________________________________________________________________    11      12  13  14  15 16  17  18  19  20                                     __________________________________________________________________________    SiO.sub.2                                                                         57.3                                                                              57.4                                                                              56.5                                                                              56.8                                                                              54.3                                                                             55.8                                                                              57.8                                                                              72.8                                                                              77.3                                                                              76.6                                   Al.sub.2 O.sub.3                                                                  9.3 9.3 9.4 9.4 8.1                                                                              8.4 9.6 0.25                                                                              1.7 1.9                                    B.sub.2 O.sub.3                                                                   21.2                                                                              19.1                                                                              19.0                                                                              19.1                                                                              24.2                                                                             24.9                                                                              19.4                                                                              21.2                                                                              13.8                                                                              14.2                                   Li.sub.2 O                                                                        --  1.5 1.1 1.1 -- 2.6 1.1 0.4 --  --                                     Na.sub.2 O                                                                        8.8 4.4 8.5 8.5 11.4                                                                             6.3 8.6 1.2 4.4 4.5                                    K.sub.2 O                                                                         --  4.8 1.5 1.5 -- --  1.5 1.4 --  --                                     WO.sub.3                                                                          1.6 1.6 --  --  -- --  --  --  --  --                                     SnO.sub.2                                                                         0.31                                                                              0.31                                                                              0.93                                                                              0.54                                                                              0.56                                                                             0.58                                                                              0.63                                                                              0.58                                                                              0.35                                                                              0.35                                   CuO 0.40                                                                              0.40                                                                              0.81                                                                              0.82                                                                              0.42                                                                             0.43                                                                              0.83                                                                              0.53                                                                              0.41                                                                              0.41                                   Cl  0.60                                                                              0.60                                                                              0.25                                                                              0.25                                                                              0.60                                                                             0.60                                                                               -- 0.98                                                                              0.74                                                                              0.74                                   Br  0.40                                                                              0.40                                                                              0.25                                                                              0.25                                                                              0.40                                                                             0.40                                                                              0.50                                                                              0.74                                                                              0.49                                                                              0.49                                   F   --  --  1.85                                                                              1.85                                                                              -- --  --  --  0.74                                                                              0.74                                   __________________________________________________________________________

A comparison of Examples 13 and 14 shows the effect of tin oxidementioned earlier. Likewise, a comparison of Examples 15 and 16illustrates the effect of shifting alkali metal oxide contents.

TABLE 3 sets forth compositions of three glasses that are identical incomposition, except for CuO content. It also gives the R-value for thecompositions, as well as the UV cut off characteristics of the glasses.

                  TABLE 3                                                         ______________________________________                                        Oxide      A            B       C                                             ______________________________________                                        SiO.sub.2  49.00        49.00   49.00                                         Al.sub.2 O.sub.3                                                                         9.00         9.00    9.00                                          B.sub.2 O.sub.3                                                                          22.80        22.80   22.80                                         Li.sub.2 O 6.50         6.50    6.50                                          Na.sub.2 O 10.40        10.40   10.40                                         K.sub.2 O  1.60         1.60    1.60                                          WO.sub.3   0.07         0.07    0.07                                          As.sub.2 O.sub.3                                                                         0.20         0.20    0.20                                          SnO.sub.2  --           --      --                                            CuO        0.36         0.20    0.28                                          Cl         0.40         0.40    0.40                                          Br         0.40         0.40    0.40                                          R-value    0.42         0.42    0.42                                          UV cutoff  Yes          No      Weak                                          ______________________________________                                    

As indicated, the glass having a CuO content of 0.36% [˜0.20% Cu₂ O](Glass A) does have a sharp UV transmission cutoff at 400 nm, thusindicating the presence of a copper halide crystal phase. The glass with0.28% CuO [˜0.16% Cu₂ O] (Glass C) showed weak absorption at wavelengthsof 325-400 nm. The glass with a CuO content of 0.20% [˜0.11% Cu₂ O](Glass B) exhibited essentially no significant absorption of radiationabove 325 nm, thus indicating no precipitation of a copper halide phase.

The FIGURE in the attached drawing renders the comparison even morevividly. This FIGURE is a graphical representation wherein wavelength innm is plotted along the horizontal axis, and degree of absorption (ABS)is plotted along the vertical axis. The three curves are based onabsorption measurements made on samples of the three glasses of TABLE 3.The curves are identified by the example numbers in TABLE 3. It will beobserved that the curve for glass A, the 0.36% CuO glass, has a sharptransmission cutoff at about 400 nm. Curve C indicates a weak absorptionand cutoff, while curve B indicates essentially no absorption aboveabout 325 nm.

TABLE 4 sets forth compositions in cation percent for several glasseshaving different R-values due to variations in R₂ O, RO and B₂ O₃contents, and the consequent effects on UV cutoff. The TABLE sets forththe R-value, the UV cutoff at 400 nm and the color for each glass.

                  TABLE 4                                                         ______________________________________                                        D           E       F       G     H     I                                     ______________________________________                                        SiO.sub.2                                                                             47.00   47.00   47.00 36.90 46.00 44.10                               Al.sub.2 O.sub.3                                                                      9.00    9.00    9.00  12.60 4.40  9.00                                B.sub.2 O.sub.3                                                                       30.00   27.00   24.50 27.80 27.80 27.80                               Li.sub.2 O                                                                            --      5.00    --    --    6.00  --                                  Na.sub.2 O                                                                            14.00   7.00    19.50 15.80 6.80  12.20                               K.sub.2 O                                                                             --      5.00    --    --    3.00  --                                  CaO     --      --      --    1.50  --    1.50                                BaO     --      --      --    1.50  --    1.50                                WO.sub.3                                                                              0.35    0.35    0.35  --    --    --                                  ZrO.sub.2                                                                             --      --      --    2.50  4.60  2.50                                SnO.sub.2                                                                             0.10    0.10    0.10  0.16  0.16  0.16                                CuO     0.25    0.25    0.25  0.25  0.25  0.25                                Cl      0.60    0.60    0.60  0.50  0.50  0.50                                Br      0.40    0.40    0.40  0.50  0.50  0.50                                R-value 0.17    0.30    0.42  0.24  0.24  0.24                                UV      Yes     Yes     No    No    Yes   Yes                                 cutoff                                                                        Color   Yellow  Green   Green Color-                                                                              Color-                                                                              Color-                                                            less  less  less                                ______________________________________                                    

Glass F of TABLE 4 exhibits no UV cutoff. This indicates the combinedeffect of lithia being absent and the R-value being high. In contrast,glasses D and E do exhibit strong UV absorption. The distinctions arethat glass E has a Li₂ O content, while glass D has a low R-value due toa high B₂ O₃ content and a diminished Na₂ O content.

Glass G does not exhibit a UV cutoff, whereas glasses H and I, whichhave the same R-value, do. Glasses G and I illustrate the importance ofmaintaining the levels of alumina and silica within the prescribedranges even for glasses in which the R-value is maintained near anoptimal value.

TABLE 5 sets forth compositions in cation percent for several glassesembodying small composition changes. These glasses illustratecompositional changes that can be made to render a glassnon-photochromic.

                  TABLE 5                                                         ______________________________________                                        J         K      L      M    N    O    P     Q                                ______________________________________                                        SiO.sub.2                                                                            46.00  46.00  46.00                                                                              47.00                                                                              47.00                                                                              47.00                                                                              46.00 46.00                          Al.sub.2 O.sub.3                                                                     10.50  10.50  10.50                                                                              9.00 9.00 9.00 9.00  9.00                           B.sub.2 O.sub.3                                                                      23.80  23.80  23.80                                                                              27.00                                                                              27.00                                                                              28.00                                                                              30.00 30.00                          Li.sub.2 O                                                                           6.25   6.25   6.25 --   --   --   --    --                             Na.sub.2 O                                                                           11.00  11.00  11.00                                                                              17.00                                                                              17.00                                                                              16.00                                                                              14.00 7.00                           K.sub.2 O                                                                            1.50   1.50   1.50 --   --   --   --    7.00                           WO.sub.3                                                                             --     --     --   0.35 0.35 --   --    --                             As.sub.2 O.sub.3                                                                     0.50   0.50   0.50 --   --   --   --    --                             SnO.sub.2                                                                            --     --     --   0.20 0.12 0.12 0.10  0.10                           CuO    0.50   0.50   0.35 0.25 0.25 0.25 0.20  0.20                           CdO    --      --    --   --   --   --   0.75  0.75                           F      1.00   1.00   2.00 --   --   --   1.21  1.21                           Cl     0.25   0.60   0.25 0.60 0.60 0.60 1.60  1.60                           Br     0.25   0.40   0.25 0.40 0.40 0.40 --    --                             R-value                                                                              0.35   0.35   0.35 0.30 0.30 0.25 0.167 0.167                          Photo- Yes    No     No   No   Yes  No   Yes   No                             chromic                                                                       ______________________________________                                    

In TABLE 5, glass J is a photochromic glass. It may be renderednon-photochromic by increasing the halogen content, as illustrated byglass K. It may also be rendered non-photochromic by decreasing the Cu₂O level, as illustrated by glass L.

Glass N is also a photochromic glass that may be renderednon-photochromic by minor compositional changes. Glass M illustrates theeffect of a small increase in SnO₂ content. Care must be taken not toincrease the SnO₂ content to the point where reduction to copper metaloccurs. Glass O illustrates achieving the same end by diminishing theR-value by shifting the Na₂ O and B₂ O₃ contents. Examples M, N, and Oare also of interest in illustrating the contribution of WO₃ tophotochromism. Examples P and Q exhibit UV cutoff and demonstrate thatCdO can promote photochromism in certain glass compositions such thatits use must be restricted to low values, if present at all.

We claim:
 1. A non-photochromic R₂ O--B₂ O₃ --SiO₂ glass which containsa precipitated cuprous or cuprous-cadmium halide crystal phase and has asharp spectral cutoff at about 400 nm, the glass composition consistingessentially of, in cation percent, 35-73% SiO₂, 15-45% B₂ O₃, 0-12% Al₂O₃, the Al₂ O₃ being less than 10% when the SiO₂ is over 55%, 0-12% Li₂O, 0-20% Na₂ O, 0-12% K₂ O, the Li₂ O+Na₂ O+K₂ O being 4.75-20%, 0-5%CaO+BaO+SrO, 0.125-1.0% Cu₂ O, 0-1% CdO, 0-5% ZrO₂, 0-0.75% SnO₂, 0-1%As₂ O₃ and/or Sb₂ O₃, the glass containing 0-1.75% Cl, 0-1.0% Br,0.25-2.0% Cl+Br and 0-2% F, the contents of Cl, Br, and F being inpercent by weight of the total content of the glass composition, andhaving an R-value, calculated in mole percent, of 0.15-0.45, the R-valuenot exceeding 0.30, except as the glass composition meets at least onecondition selected from the group: up to 12 cation % Li₂ O, less than 10cation % Al₂ O₃, at least 0.3 cation % Cu₂ O and 0.50-2.0% Cl+Br.
 2. Aglass in accordance with claim 1 wherein the glass contains ZrO₂, in anamount effective to increase the refractive index of the glass.
 3. Aglass in accordance with claim 1 wherein the glass contains CaO+BaO+SrOin an amount effective to increase the refractive index of the glass. 4.A glass in accordance with claim 1 wherein the glass contains Li₂ O inan amount effective to provide a sharp UV cutoff at 400 nm.
 5. A glassin accordance with claim 1 wherein the glass contains 0.125-0.5 cation %Cu₂ O, the amount present being effective to provide a sharp UV cutoffat 400 nm.
 6. A glass in accordance with claim 1 wherein the glass hasan R-value less than that sufficient to inhibit precipitation of acuprous chloride phase in the glass.
 7. A glass in accordance with claim1 wherein the glass contains 2-12% Al₂ O₃, the amount present beinginsufficient to be deleterious to UV absorption.
 8. A glass inaccordance with claim 5 wherein the Cu₂ O content is 0.2-0.5 cationpercent.
 9. A glass in accordance with claim 1 wherein the content ofCl+Br is 0.5-1.5% by weigh of the total content of the glasscomposition.
 10. A glass in accordance with claim 1 wherein the glasshas no fixed tint and its composition consists essentially of 40-70%SiO₂, 20-35% B₂ O₃, 2-10% Al₂ O₃, 8-20% R₂ O selected from 0-12% Li₂ O,O-20% Na₂ O and 0-12% K₂ O, 0.2-0.5% Cu₂ O and Cl and/or Br, the contentof Cl and/or Br being 0.5-1.5% by weight of the total content of theglass composition.
 11. A glass in accordance with claim 1 containing upto 1% of a transition metal oxide whereby a fixed tint is imparted tothe glass.
 12. A glass in accordance with claim 1 containing up to 2% ofan oxide selected from the group consisting of TiO₂, Nb₂ O₃, and PbO,and/or up to 0.5% of an oxide selected from the group consisting of WO₃and MoO₃, whereby refractive index is enhanced and a fixed tint isimparted to the glass.
 13. A glass in accordance with claim 1 wherein aportion of the copper content is in the cupric state, the amount ofcopper in the cupric state being sufficient to impart a fixed tint tothe glass.
 14. A glass in accordance with claim 1 wherein a portion ofthe copper content is in a colloidal state, the amount of copper in thecolloidal state being sufficient to impart a fixed tint to the glass.